60-70% of the concrete lump produced from demolished structures is presently crushed and reused for subbase course of roads, and the rest is discarded. The amount of the demolished concrete is estimated to be 3 to 5 times of the present amount in next decade. The reuse for subbase course will be difficult and recycling of concrete from structure to structure is necessary. In this paper, outline of a technology developed to produce high quality recycled aggregate that satisfy the quality required in JIS A 5005 (crushed stone) and JASS 5 (gravel) is presented. Properties of the concrete using the aggregate were shown to have the same quality as that made by natural aggregates such as gravel and crushed stone.

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This study experimentally investigated how to make 300N/mm 2 ultra-high-strength concrete. The fine aggregate type was found to significantly influence compressive strength development, and the use of quartz fine aggregates yielded the highest strength. The strength of the mortar specimens made of blended cement containing silica fume reached 350-400N/mm 2 with a two-stage heat curing scheme. For concrete, the type and maximum size of coarse aggregates greatly affect the strength; the use of rhyolites up to 10mm resulted in approximately 300N/mm 2. The use of homogenous high-strength aggregates does not necessarily yield high concrete strength, likely due to the difference in Poisson's ratio.

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